I have three questions, the first would be "What is the difference between to chase sth and to chase after sth?", the second is "Can I say "Now I can finally lift this mask", in the sense that I take it off?" and for the third you will have to read through the following lines:

Nothing is like it was before
I know not who I am anymore
Chasing something that's behind me
When will I be set free?

Don`t you actually have to say "I do not know who I am anymore"? The band is American, so it cannot be a mistake, but this is completely new to me, I´d be very happy if someone could explain this to me :)

I always advise my students to avoid thinking about grammar when looking at poetry or lyrics. The usual rules are not always applied because the writer needs to make the words fit the beat of the music or the rhythm of the poem.

In short, none of these structures are wrong, but that doesn't mean they are common in everyday English.